Electromechanical timers are commonly used in appliances such as dishwashers, washing machines and dryers for controlling the sequential energization and de-energization of electrical components in the appliance to provide the desired cyclical operations. Frequently, such timers require axial movement of the control knob, such as by pushing or pulling the knob. In such timers a control knob mounted for rotation with the control cam-carrying shaft of the timer is manually axially displaced to close a timer motor control switch which is a separate switch provided in addition to the control cam actuated timer switches. Typically, in such arrangements the control knob is retained in its displaced position to maintain motor energization until at or near the end of the operating cycle. Mechanical means are provided to reset the knob to its original position, thereby deactuating the separate switch and ending the cycle.
In some such timers, the timer is deactuated prior to completing a full 360.degree. rotation in order to insure deactuation before the shaft reaches an actuation point so as to prevent repeated cycling. This creates a rotational dead space which is overcome by employing manual rotation of the control knob to an initial position prior to axial displacement.
U.S. Pat. No. 3,264,441 to Jenkins addressed the problem of eliminating the need for manual rotation by providing a push to start arrangement in which the control knob is automatically positioned at the actuation point of the timer at the end of the cycle without perpetual Cycling. As taught by Jenkins, the cycle is started by pushing in the control knob which is mounted to the cam-carrying control shaft to close the separate motor control switch. The knob is held in this position by engagement with the mounting frame, until the end of the cycle at which time an index means mounted to the control shaft becomes aligned with an aperture in the frame permitting axial outward movement of the knob and shaft to its original position, thereby deactuating the motor control switch and terminating the cycle.
Another push to start arrangement known in the art provides for actuation of the separate motor control switch by an axial cam and slider arrangement. In this arrangement, as the control knob is pushed in, an axial cam coupled to the control knob engages a slider and moves it radially outward to actuate the separate switch. The control knob is held in its displaced position by a yielding retaining spring until late in the cycle. At that time, a reset cam surface projecting from the control shaft engages a camming shoulder which urges the shaft outwardly, overcoming the retainer spring and moving of the shaft to its initial, outward position; thereby deactuating the separate switch. In this arrangement one of the cam actuated timer switches is employed as a reset switch in order to maintain continuity during the mechanical reset to assure that the control shaft reset cam has completely cleared the camming shoulder and returned to its initiation point for subsequent actuation. This need for a reset switch is particularly disadvantageous in multicycle appliances since additional switches would likely be required in the selector switch bank to maintain cycle and circuit integrity.
It is therefore an object of the present invention to provide a timer of the type actuated by axial movement of the control knob which eliminates the need for a separate motor control switch, the need for mechanical reset near the end of the operating cycle, and the need for manual rotation of the control knob prior to axial displacement.
It is a further object of the present invention to provide a timer of the aforementioned type which eliminates the need for a reset switch.
It is a further object of the present invention to provide a timer of the aforementioned type for multicycle appliances which eliminates the need for an extra switch or switches in the cycle selector switch bank to maintain cycle and circuit integrity.
It is a further object of the present invention to provide a push to start arrangement in a timer which is relatively simple, inexpensive and reliable.